Derive gaussian splat SH order from resource layout

engine/src/Rendering/Passes/BuiltinGaussianSplatPass.cpp

@@ -1064,6 +1064,11 @@ bool BuiltinGaussianSplatPass::PrepareVisibleGaussianSplat(
 
     commandList->SetPipelineState(pipelineState);
 
+    const float shOrder =
+        visibleGaussianSplat.gaussianSplat != nullptr
+            ? static_cast<float>(visibleGaussianSplat.gaussianSplat->GetSHOrder())
+            : 0.0f;
+
     const PerObjectConstants perObjectConstants = {
         sceneData.cameraData.projection,
         sceneData.cameraData.view,
@@ -1080,7 +1085,7 @@ bool BuiltinGaussianSplatPass::PrepareVisibleGaussianSplat(
         Math::Vector4(
             static_cast<float>(cachedGaussianSplat->splatCount),
             static_cast<float>(workingSet->sortCapacity),
-            3.0f,
+            shOrder,
             0.0f)
     };
 

engine/src/Resources/GaussianSplat/GaussianSplat.cpp

@@ -3,6 +3,38 @@
 namespace XCEngine {
 namespace Resources {
 
+Core::uint32 ResolveGaussianSplatSHOrderFromCoefficientCount(Core::uint32 coefficientCount) {
+    if (coefficientCount == 0u || (coefficientCount % kGaussianSplatSHColorChannelCount) != 0u) {
+        return 0u;
+    }
+
+    Core::uint32 remainingTriplets = coefficientCount / kGaussianSplatSHColorChannelCount;
+    Core::uint32 resolvedOrder = 0u;
+    for (Core::uint32 order = 1u; order <= kGaussianSplatMaxSHOrder; ++order) {
+        const Core::uint32 bandTriplets = (2u * order) + 1u;
+        if (remainingTriplets < bandTriplets) {
+            break;
+        }
+
+        remainingTriplets -= bandTriplets;
+        resolvedOrder = order;
+    }
+
+    return resolvedOrder;
+}
+
+Core::uint32 ResolveGaussianSplatSHOrderFromSectionStride(Core::uint32 elementStride) {
+    if (elementStride < sizeof(float)) {
+        return 0u;
+    }
+
+    const Core::uint32 floatCount = elementStride / static_cast<Core::uint32>(sizeof(float));
+    const Core::uint32 coefficientCount = floatCount > kGaussianSplatSHCoefficientCount
+                                              ? kGaussianSplatSHCoefficientCount
+                                              : floatCount;
+    return ResolveGaussianSplatSHOrderFromCoefficientCount(coefficientCount);
+}
+
 GaussianSplat::GaussianSplat() = default;
 
 GaussianSplat::~GaussianSplat() = default;
@@ -69,6 +101,11 @@ const GaussianSplatSHRecord* GaussianSplat::GetSHRecords() const {
     return static_cast<const GaussianSplatSHRecord*>(GetSectionData(GaussianSplatSectionType::SH));
 }
 
+Core::uint32 GaussianSplat::GetSHOrder() const {
+    const GaussianSplatSection* shSection = FindSection(GaussianSplatSectionType::SH);
+    return shSection != nullptr ? ResolveGaussianSplatSHOrderFromSectionStride(shSection->elementStride) : 0u;
+}
+
 bool GaussianSplat::ValidateSections(const Containers::Array<GaussianSplatSection>& sections,
                                      size_t payloadSize) const {
     for (size_t index = 0; index < sections.Size(); ++index) {